1. Field of the Invention
This invention relates generally to rotary cutting tools and end mills, and more particularly to helically fluted end mills having variable helical angles for improved performance characteristics.
2. Description of Related Art
Rotary cutting tools are used for various machining operations on workpieces. An end mill cutter or “end mill” is a type of rotary cutting tool. Machine operations often carried out using an end mill cutter include the forming of slots, keyways, and pockets. During typical use of an end mill cutter, a milling machine rotatably drives the end mill cutter about its longitudinal axis, and various cutting edges of the end mill cutter are used to remove material from a workpiece.
Over time, the cutting edges of an end mill cutter become dull due to physical contact between the end mill cutter and workpieces. As the cutting edges become dull, internal stresses generated within the end mill cutter during use increase. Harmonic vibrations constitute major sources of internal stresses in end mill cutters. It is common for end mill cutters to break during use due to the internal stresses. One way of extending the operation life of a end mill cutter is to reduce the amplitudes of harmonic vibrations generated within the tool during use.
It would thus be beneficial to have an end mill cutter wherein amplitudes of harmonic vibrations generated within the tool during use are reduced. The operational life of such an end mill cutter would expectedly be extended significantly.
The state of the art includes the following:
Hiyama, U.S. Pat. No. 4,963,059, teaches a rotary cutting tool that includes four axial flutes. The four axial flutes have cutting edges that form two symmetrical pairs. Each of the pairs has a different helix angle from the another pair. Furthermore, the cutting edges are all equally spaced from one another at one point along the length of the cutting tool.
Noland, U.S. Pat. No. 6,991,409, teaches a rotary cutting tool that includes four axial flutes that extend from an end surface to a fluted cutting end and each includes a cutting edge. The cutting edges are unequally spaced along the circumference of the end surface lying in a plane perpendicular to the longitudinal axis of rotation. In addition, all cutting edges are of a different helix from one another and the cutting edge geometries vary from one another to create a different sound pattern that reduces resonant harmonic vibrations.
While Hiyama teaches two pairs of symmetrical flutes that differ from each other, and while Noland teaches all four flutes being variable, neither teaches the optimum combination of one symmetrical pair of flutes and two flutes with different helix angles.
Flynn, et al, U.S. 2003/0118411 A1, teaches an end mill that include a flute having a helix which varies along the length of the tool. The end mill may include varying numbers of flutes, whether odd or even; helix change(s) within a flute or between flutes; or indexing between cutting edges or flutes. A ‘slow’ or ‘high’ helix may be used at the end or starting point of the tool, depending upon the application. A slow helix at the end or starting point is desirable for a strong corner in ramping and plunging into the material. When a higher helix is used at the end transitioning to a smaller helix at the shank, the corner is also protected because of the helix change. The high helix at the tip may be needed for shearing action in a given material.
Risen, Jr., U.S. Pat. No. 6,652,203 B1, teaches a precision drill bit that includes at least one cutting flute extends along the length of the bit and exhibits a helix angle of about 38 degrees at the tip. The helix angle decreases to an angle of about 15 degrees at the end of the flute run-out. The helix angle changes progressively and substantially linearly over a number of segments along the length of the drill bit.
Ito, U.S. 2003/0185640 A1, teaches a dual rake twist drill bit for drilling holes in articles made of abrasive materials (fiberglass-filled printed circuit boards, which relatively quickly dull bits). The bit includes spiraled flutes with cutting lips and inclined to the axis of the bit at a relatively small helix angle or rake in the range of about 3 degrees to 10 degrees. A longer rear portion which the flutes and cutting lips have a larger rake of about 33 degrees. The dual rake bit has substantially greater wear resistance than single rake bits. In a modification of the dual rake bit, the central web portion has a front longitudinal portion which is relatively acutely tapered, and a rear portion which is relatively modestly tapered, the dual tapered construction increasing resistance of the bit to breaking.
Walrath, U.S. 2004/0057803 A1 and U.S. 2004/0258490, teach a rotary end-mill having a deferential flute construction with all individual flutes being unequally spaced about the circumference of the cylindrical tool body at different helix angles. The cutting edge of these flutes also face in the direction of tool rotation.
Other references of interest include the following: C. O. Graves, U.S. Pat. No. 2,782,490; H. P. Brumell et al, U.S. Pat. No. 1,963,611; Kuberski, U.S. Pat. No. 5,779,399; George, U.S. Des. 445,436; Kouvelis, U.S. Des. 430,584; and Nishimura, U.S. Des. 328,557.
All of the above-described references are hereby incorporated by reference in full.